Fix some warnings on latest nightly

Unfortunately I cannot test this because of several ICEs :(

Author: Techcable

libs/context/src/lib.rs

@@ -1,7 +1,6 @@
 #![feature(
     negative_impls, // !Send is much cleaner than `PhantomData<Rc>`
     untagged_unions, // I want to avoid ManuallyDrop in unions
-    const_fn_trait_bound, // So generics + const fn are unstable, huh?
     generic_associated_types, // Finally!
     const_trait_impl,
     ptr_metadata

src/epsilon/handle.rs

@@ -59,8 +59,7 @@ zerogc_derive::unsafe_gc_impl!(
 );
 
 unsafe impl HandleCollectorId for EpsilonCollectorId {
-    type Handle<T> 
-        where T: GcSafe<'static, Self> + ?Sized = GcHandle<T>;
+    type Handle<T> = GcHandle<T> where T: GcSafe<'static, Self> + ?Sized;
 
     fn create_handle<'gc, T>(_gc: Gc<'gc, T, Self>) -> Self::Handle<T::Branded>
         where T: GcSafe<'gc, Self> + GcRebrand<'static, Self> + ?Sized {

src/lib.rs

@@ -8,10 +8,8 @@
     once_cell, // RFC 2788 (Probably will be accepted)
     negative_impls, // More elegant than marker types
     alloc_layout_extra,
-    const_fn_fn_ptr_basics,
     const_mut_refs,
     const_option,
-    const_fn_trait_bound, // NOTE: Needed for the `epsilon_static_array` macro
     const_trait_impl, // EXPERIMENTAL: const Deref
     const_slice_from_raw_parts,
     const_transmute_copy,